On Mavericks, Cmd-Tab works as expected just fine (selecting the next application in the MRU list). With the task selector open, I can hit shift as well to move back in the same list before selecting app.
As soon as I plug in a second monitor (with it's own "space" I assume), this suddenly works differently. When I activate the task selector with Cmd-Tab, it opens as usual, but as soon as I hit shift in addition, the task selector closes, selecting whatever was selected when I hit shift.
On dual screen I can start the task selector up with either Cmd-Tab or Cmd-Shift-Tab, but as soon as I add or remove shift from it, it selects the application underneath and closes the task selector. On a single screen, I can move back and forth without anything getting selected until I release Cmd-Tab as well.
Does anybody know if this is a bug or the way it is supposed to be, and if the latter, what is the rationale for this?